Generally, in a numerical controller of a machine tool, by performing the relative movement of the tool relative to the work, by operating either or both of a translation driving shaft (a straight line driving shaft such as the X axis, the Y axis and the Z axis) and a rotation driving shaft (a tool rotation driving shaft or a table rotation driving shaft such as an A axis, B axis and a C axis) included in the machine tool according to a processing program, the control is performed so as to process a predetermined processing shape. At this time, the processing program includes a case of directly instructing the movement of each driving shaft, and a case of instructing the relative movement of the tool relative to the work to convert the relative movement into the movement of each driving shaft in the numerical controller.
In the controlling of a machine, which includes a rotation driving shaft also capable of changing a posture of the tool with respect to the work, like the five-axis processing machine, in a case of using the latter method mentioned above, that is, the method of instructing the relative movement of the tool relative to the work to the processing program to convert the relative movement into the movement of each driving shaft in the numerical controller, there is a problem as below.
In addition, herein, the expression instructing the relative movement of the tool relative to the work to the processing program refers to a case of moving a tool tip point actually performing the processing with respect to the work, and instructing the relative position and the posture of the tool tip point relative to the work and a relative feeding speed of the tool tip point relative to the work to the processing program (generally, referred to as tool tip point control).
That is, for example, in the case of performing the movement instruction which performs a great tool posture change when the movement of the position of the tool tip point is small in the processing program, if the feeding speed of the tool tip point is constantly maintained with respect to the work, the great tool posture change is generated in a short time, whereby the speed of the rotation driving shaft is rapidly increased, and in addition, the speed of the translation driving shaft is also rapidly increased. Otherwise, as another example, even if the tool posture change to be instructed to the processing program is small, in a case where the tool posture approaches a peculiar point in the five-axis processing machine, the great tool posture change is generated, and similarly, the speeds of the rotation driving shaft and the translation driving shaft are rapidly increased. In this manner, when the speed of each driving shaft is rapidly changed, there is a risk such as mechanical collision and contact with an operator, and there is a problem in that mechanical vibrations and excessive energy consumption are caused.
The peculiar point generally refers to a state where a function of a degree of freedom of a specific direction is lost, and in the case of a machine tool including a rotation shaft, the peculiar point refers to a position (an angle) in which the tool posture relative to the work is not changed even if any rotation driving shaft is moved.
For this reason, there is a technique which controls the feeding speed so as to be automatically lowered in an inner portion of a numerical controller so as not to exceed the maximum speed allowed (generally, referred to as a rapid-feeding speed or a cutting clamp speed) (see Patent Citation 1).
Moreover, separate from the relative feeding speed of the tool tip point relative to the work, there is a technique which instructs the tool posture speed (see Patent Citation 2).